Happy to help! 
Randy did a great job answering exactly that question yesterday. Take a look at it here: Where are saved files? - #4 by randyzwitch
Essentially, it’s better to write your data to a persistent location such as Google Drive or Amazon S3. Files written to the local container on Streamlit Sharing can be overwritten at any time and are not expected to persist.
Randy also linked to an example of how one would go about writing files to a persistent location:
https://medium.com/@annissouames99/how-to-upload-files-automatically-to-drive-with-python-ee19bb13dda
Best, 
Snehan